Description of the Prior Art
In the process of manufacturing ICs, the technique is known of superimposing various different films on top of a substrate of a substance such as silicon, then, using a plasma of a gas such as carbon tetrafluoride, perform dry etching to selectively remove parts of those films. Many different dry etching methods have been developed for this purpose, but the isotropy and high levels of selectivity of chemical dry etching methods make the widely used. In each of these chemical dry etching methods, a reactive gas is excited by microwaves in a plasma generation device to create an activated material, then this activated material is sent to a reaction chamber separated from the plasma chamber to react with, and hence etch, a workpiece within the reaction chamber, so the choice of reactive gas used for the etching is an important keypoint of such methods.
It is conventional practice to a use a mixture of carbon tetra-flouoride (CF.sub.4), oxygen (O.sub.2),k and nitrogen (N.sub.2) as this reactive gas.
However, this conventional technique of using a gas mixture of carbon tetrafluoride, oxygen, and nitrogen as the reactive gas causes a problem when the workpiece to be etched is a silicon nitride film, in that is difficult to selectively etch the silicon nitride film and not a silicon oxide film thereunder.
The present invention solves the above problem of the prior art, and it provides a dry etching method in which the selectively between a workpiece being etched and a substance below the workpiece is increased.